#include <vector>
using namespace std;
class Solution
{
public:
    int peakIndexInMountainArray(vector<int> &arr)
    {
        int left = 0, right = arr.size() - 1;
        while (left < right)
        {
            int mid = left + right >> 1;
            if (arr[mid] > arr[mid + 1])
                right = mid;
            else
                left = mid + 1;
        }
        return left;
    }
};